1. Field of the Invention
The invention relates to a method for manufacturing an optical display device including an optical display unit and an optical film that includes a polarizing plate and is bonded to the optical display unit and to a material roll for use in the method.
2. Description of the Related Art
A conventional method for manufacturing an optical display device such as a liquid crystal panel includes previously forming an optical film including a polarizer into a unit shape for a liquid crystal cell or the like by stamping, and bonding the unit shape to the liquid crystal cell or the like. In addition, a pre-cut optical film used in this method can not avoid an increase in the cost by a multi process and an increase in manufacturing management cost by the storage and the management. This is because it requires, for example, end face processing to suppress the overflow of the adhesive from the end face, packing in the clean room atmosphere to avoid dust and dirt, the problem of the dirt and scratch caused while transporting to the next process (for instance, bonding process for the panel), the inspection process accompanied with the problem, and the management for the stock of each kind of the liquid crystal cells. Moreover, bonding of the pre-cut optical film to the liquid crystal cell is done by the batch process. In the batch process of bonding, the pre-cut optical film is adjusted for its position one by one and then bonded to the liquid crystal cell. Therefore, the speed of the bonding cannot be raised, and a high-speed, continuous production becomes impossible. In addition, there are problems on dirt and contamination with the adhesive at the end face, because the optical films are stored in the form of stacking the end faces respectively. These problems cause the cost of the liquid crystal panel manufacturing to be increased as well as the cost of manufacturing the pre-cut optical film.
Therefore, there are proposed various methods including winding a long optical film such as a long polarizing plate into a roll, feeding and cutting the film from the roll, and continuously performing bonding of the cut piece. The continuous bonding method is useful, because the optical film being fed can be inspected and examined on the line and then bonded while defective portions are removed, so that the quality of the liquid crystal panel can be improved. The methods described below are known to include the steps of inspecting a long optical film on the line and bonding the optical film in such a manner, while removing defective portions of the optical film by cutting (see for example Japanese Patent Application Laid-Open Nos. 57-052017 and 2007-140046).
Japanese Patent Application Laid-Open No. 57-052017 discloses a method for manufacturing an optical display device, including unwinding and feeding a long sheet material from a roll thereof, wherein the long sheet material includes an optical film, a pressure-sensitive adhesive layer and a release film, inspecting the optical film for defects, sequentially cutting part of the long sheet material other than the release film into pieces each with a length corresponding the size of an optical display unit (when a defect is detected, the cutting is performed again at a place immediately behind the position of the defect), removing defect-containing short parts of the optical film, and then bonding each of the remaining optical films to the surface of the optical display unit.
However, such a defect inspection is performed using a mechanism in which a defective portion is removed by cutting when a sensor detects it, and therefore, when a plurality of defects exist in regions close to one another, the process of cutting the optical film is interrupted due to each response of the sensor to each defect. After all, defects in regions close to one another cause the problem of a reduction in bonding speed. In particular, this method is unsuitable for production of large-screen televisions, the yield of which is required to be high.
Japanese Patent Application Laid-Open No. 2007-140046 discloses a method including stamping or cutting an optical film into the desired size in such a manner that defective portions can be separated based on the result of defect inspection. In this method, however, a release film that protects a pressure-sensitive adhesive layer is also cut at the same time, and therefore, the step of bonding the film to a liquid crystal cell has to be performed in a batch mode. There has also been the issue of how to control the cutting width for removal of defective portions in the case that a plurality of defects exists in regions close to one another.
In this regard, there is proposed a method of working an optical film such as a polarizing plate, which includes determining whether each area of the film is defective or not, based on the result of the inspection of each area, and performing stamping or the like in such a manner the positions of defects can be separated (Japanese Patent No. 3974400). This method may also be taken into account.